Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor to compress air that is drawn into the engine and a turbine to capture energy associated with the combustion of a fuel-air mixture. Referring to FIG. 2A, the fuel-air mixture may form part of a primary/core flow 202 and may be used to generate thrust. The products of combustion may be at elevated temperatures, which may cause the turbine components to see temperatures as hot as 2000 degrees Fahrenheit (approximately 1093 degrees Celsius).
At least a portion of one or more secondary flows (denoted in FIG. 2A by arrows 208) may provide cooling air to turbine components. The air 208 may be sourced from, e.g., the compressor. Since the amount of air 208 diverted to provide cooling impacts the performance/efficiency of an engine, seals (see FIG. 2B—seal 254) are incorporated as part of a secondary flow system to reduce (e.g., minimize) leakage.
Referring to FIG. 2B, a conventional two-point axial ring seal 254 is shown. The seal 254 is commonly referred to as a dog-bone seal and operates as a mechanical, non-linear spring. An axial interference fit is provided between the seal 254 and adjacent components (e.g., component 258), which causes the seal to be subject to a rolling motion. For example, the ends 254a and 254b of the seal 254 may be subject to a rolling motion, where the end 254a may be urged aft and the end 254b may be urged forward in FIG. 2B. As the two ends 254a and 254b deflect elastically to new locations (e.g., new diameters), hoop stress is introduced which acts in a restorative manner. For example, elastic restorative forces imposed on the ends 254a and 254b are shown via arrows 264a and 264b, respectively.
Ideally, the seal 254 maintains contact with the adjacent components (e.g., the component 258, component 268) despite axial motion and a pressure differential that urges the seal 254 to lose contact with the components. For example, a pressure load 270 may be imposed on the seal 254, where the load 270 is a result of the secondary flows 208 being at an elevated pressure.
Given that the seal 254 is often in contact with extremely hot components, such as for example at the interface between the end 254b and the component 258, the functional or structural integrity of the seal 254 may be compromised due to creep. Creep occurs when the material of the seal 254 is subjected to elevated stress (e.g., elevated temperature) for extended periods of time. Creep causes the material of the seal 254 to permanently deform (based on the deflected state/position that the seal 254 assumes), even when the magnitude of the stress is below the material's yield strength. Creep degrades the seal 254's ability to withstand the load 270 over time, which can cause the seal 254 (e.g., the end 254b) to lose contact with an adjacent component (e.g., the component 258).